Population dynamics, delta vulnerability and environmental change: comparison of the Mekong, Ganges-Brahmaputra and Amazon delta regions

Using lake sediments to assess the long-term impacts of anthropogenic activity in tropical river deltas

Tropical river deltas, and the social-ecological systems they sustain, are changing rapidly due to anthropogenic activity and climatic change. Baseline data to inform sustainable management options for resilient deltas is urgently needed and palaeolimnology (reconstructing past conditions from lake or wetland deposits) can provide crucial long-term perspectives needed to identify drivers and rates of change. We review how palaeolimnology can be a valuable tool for resource managers using three current issues facing tropical delta regions: hydrology and sediment supply, salinisation and nutrient pollution. The unique ability of palaeolimnological methods to untangle multiple stressors is also discussed. We demonstrate how palaeolimnology has been used to understand each of these issues, in other aquatic environments, to be incorporated into policy. Palaeolimnology is a key tool to understanding how anthropogenic influences interact with other environmental stressors, providing policymakers and resource managers with a 'big picture' view and possible holistic solutions that can be implemented.

Anthropogenic-induced environmental and ecological changes in the Nile Delta over the past half-century

Anthropogenic activities over the past half-century have had a negative impact on the wetland ecosystem in the Nile Delta, which provides essential provisioning and regulating services. Therefore, it is crucial to systematically investigate pollution levels and their ecological consequences at both spatial and temporal scales in order to promote sustainable development. In this study, data on metal pollution in the Manzala Lake were compiled through a systematic review of all published literature from 1968 to 2020. Additionally, agricultural data (including land use, pesticide and fertilizer usage, and discharge) and economic data for the same time period were collected to identify the main drivers of pollution. The results indicated an overall increasing trend in heavy metal concentrations during the study period. The average concentrations of metals, arranged in descending order, were as follows: Fe (15,115.5 μg/g) > Mn (722 μg/g) > Zn (115.4 μg/g) > Cu (65.9 μg/g) > Ni (62.5 μg/g) > Cr (58.1 μg/g) > Pb (54.1 μg/g) > Cd (4.7 μg/g) > Hg (0.1 μg/g). A linear regression model revealed that wastewater discharge, water reuse, and the use of pesticides and fertilizers are the main sources of heavy metal pollution in the Manzala Lake. Consequently, there has been a dramatic decrease in the biodiversity of fish and molluscan communities. The study also found a correlation between heavy metal pollution and socio-economic development, highlighting the urgent need for attention to the conservation, management, and sustainable development of the lake.

Distribution of potentially toxic elements in soils and sediments in Pearl River Delta, China: Natural versus anthropogenic source discrimination

Although anthropogenic contamination has been regarded as the most important source of potentially toxic elements (PTEs) in soils of large river delta plains, the extent to which human activities affect PTEs in soils is worth exploring. This study used high density geochemical data to distinguish source patterns of PTEs in soils of the Pearl River Delta Economic Zone, a large industrialized and urbanized area in China. Enrichment factor, discriminant analysis, principal components analysis, cumulative distribution function, and positive matrix factorization were used to identify sources of PTEs in soils. The results indicated that parent material was the most significant factor affecting geochemical characteristics of PTEs in soils. Median concentrations of Cd, Cr, Cu, Hg, Pb, and Zn were 0.400, 88.5, 40.5, 0.143, 43.0, and 116.0 mg/kg for stream sediments, 0.333, 75.7, 39.0, 0.121, 42.6, and 98.5 mg/kg for deep soils, and 0.365, 74.0, 45.1, 0.143, 44.6, and 119.5 mg/kg for surface soils, respectively, all of which exceed relevant reference standards. Compared with stream sediments and deep soils, surface soils exhibit substantial concentrations of PTEs. Chemical weathering and erosion of parent materials distributed in the Pearl River Delta were the main sources of PTEs in soils. Diffuse contamination and many small local contamination sources distributed throughout the study area were the most significant anthropogenic sources of PTEs in surface soils. Intensive human activities failed to change the soil geochemical characteristics derived from the parent material at the regional scale. However, it could induce non-point source pollution and local severe PTEs pollution in surface soils.

Sediment delivery to sustain the Ganges-Brahmaputra delta under climate change and anthropogenic impacts

The principal nature-based solution for offsetting relative sea-level rise in the Ganges-Brahmaputra delta is the unabated delivery, dispersal, and deposition of the rivers' ~1 billion-tonne annual sediment load. Recent hydrological transport modeling suggests that strengthening monsoon precipitation in the 21st century could increase this sediment delivery 34-60%; yet other studies demonstrate that sediment could decline 15-80% if planned dams and river diversions are fully implemented. We validate these modeled ranges by developing a comprehensive field-based sediment budget that quantifies the supply of Ganges-Brahmaputra river sediment under varying Holocene climate conditions. Our data reveal natural responses in sediment supply comparable to previously modeled results and suggest that increased sediment delivery may be capable of offsetting accelerated sea-level rise. This prospect for a naturally sustained Ganges-Brahmaputra delta presents possibilities beyond the dystopian future often posed for this system, but the implementation of currently proposed dams and diversions would preclude such opportunities.

Socio-demographic backwardness in cyclone prone coastal villages: An Insight from Indian Sundarban

The capability to design for, respond to, and recover from natural hazards is much influenced by demographic and socio-economic vulnerability of the region. Triggering effect of cyclone induced multi-hazards in the coastal areas of West Bengal, India makes the life and livelihood of people miserable. Very recent cyclones, like, Fani, Bulbul, Amphan and Yaas make people much more susceptible to hazard with the evil impact of on-going pandemic. According to IPCC, sensitivity and adaptive capacity analysis at micro level is taking much importance to address the readiness situation of the region. In this backdrop, the study aims to assess and map the level of demographic and socio-economic backwardness at village level for Kakdwip coastal area under coastal West Bengal, India. Applying principal component analysis we have tried to find out the level of demographic and socio-economic backwardness at different geographical locations (categorise as inland, riverine/ estuarine, coastal and island). The final findings suggest that backwardness is more prevalent in the southern part of the research region, with island and riverine/ estuary villages being particularly vulnerable. When the results have tries to find out the triggering factors at different geographical locations, female and child population, land holdings and earning of household came as the dominant factors for such higher degree of backwardness. These findings, when combined with micro level assessments, could help village administrators, planners and policymakers, and emergency managers design more effective and spatially tailored backwardness management plans.

Vulnerability and Risk Assessment to Climate Change in Sagar Island, India

Inhabitants of low-lying islands face increased threats due to climate change as a result of their higher exposure and lesser adaptive capacity. Sagar Island, the largest inhabited estuarine island of Sundarbans, is experiencing severe coastal erosion, frequent cyclones, flooding, storm surges, and breaching of embankments, resulting in land, livelihood, and property loss, and the displacement of people at a huge scale. The present study assessed climate change-induced vulnerability and risk for Sagar Island, India, using an integrated geostatistical and geoinformatics-based approach. Based on the IPCC AR5 framework, the proportion of variance of 26 exposure, hazard, sensitivity, and adaptive capacity parameters was measured and analyzed. The results showed that 19.5% of mouzas (administrative units of the island), with 15.33% of the population at the southern part of the island, i.e., Sibpur–Dhablat, Bankimnagar–Sumatinagar, and Beguakhali–Mahismari, are at high risk (0.70–0.80). It has been concluded that the island has undergone tremendous land system transformations and changes in climatic patterns. Therefore, there is a need to formulate comprehensive adaptation strategies at the policy- and decision-making levels to help the communities of this island deal with the adverse impacts of climate change. The findings of this study will help adaptation strategies based on site-specific information and sustainable management for the marginalized populations living in similar islands worldwide.

Salinity and food security in southwest coastal Bangladesh: impacts on household food production and strategies for adaptation

The rising salinity of land and water is an important, but understudied, climate change-sensitive trend that can exert devastating impacts on food security. This mixed methods investigation combines salinity testing with qualitative research methods to explore these impacts in one of the most salinity-affected regions in the world—the Ganges River Delta. Data collection in 2015 and 2016 undertaken in Bangladesh’s southwest coastal region and Dhaka consisted of 83 in-depth household and stakeholder interviews, six community focus groups, and salinity testing of 27 soil and 45 surface and groundwater samples. Results show that household food production is a multifaceted cornerstone of rural livelihood in the southwest coastal region, and virtually every component of it—from rice plantation and homestead gardening to livestock cultivation and aquaculture—is being negatively affected by salinity. Although households have attempted multiple strategies for adapting food production, effective adaptation remains elusive. At the community level, improved irrigation and floodplain management, as well as restrictions on saltwater aquaculture to abate salinity, are viewed as promising interventions. However, the potential of such measures remains unrealized on a broad scale, as they require a level of external resources and regulation not yet provided by the NGO and government sectors. This study elucidates issues of accessibility, equity, and governance surrounding agricultural interventions for climate change-related salinity adaptation, and its findings can help inform the community of organizations that will increasingly need to grapple with salinity in order to guarantee food security in the context of environmental change.

Halotolerant Microbial Consortia for Sustainable Mitigation of Salinity Stress, Growth Promotion, and Mineral Uptake in Tomato Plants and Soil Nutrient Enrichment

Salinity significantly impacts the growth, development, and reproductive biology of various crops such as vegetables. The cultivable area is reduced due to the accumulation of salts and chemicals currently in use and is not amenable to a large extent to avoid such abiotic stress factors. The addition of microbes enriches the soil without any adverse effects. The effects of microbial consortia comprising Bacillus sp., Delftia sp., Enterobacter sp., Achromobacter sp., was evaluated on the growth and mineral uptake in tomatoes (Solanum Lycopersicum L.) under salt stress and normal soil conditions. Salinity treatments comprising Ec 0, 2, 5, and 8 dS/m were established by mixing soil with seawater until the desired Ec was achieved. The seedlings were transplanted in the pots of the respective pH and were inoculated with microbial consortia. After sufficient growth, these seedlings were transplanted in soil seedling trays. The measurement of soil minerals such as Na, K, Ca, Mg, Cu, Mn, and pH and the Ec were evaluated and compared with the control 0 days, 15 days, and 35 days after inoculation. The results were found to be non-significant for the soil parameters. In the uninoculated seedlings’ (control) seedling trays, salt treatment significantly affected leaf, shoot, root dry weight, shoot height, number of secondary roots, chlorophyll, and mineral contents. While bacterized seedlings sown under saline soil significantly increased leaf (105.17%), shoot (105.62%), root (109.06%) dry weight, leaf number (75.68%), shoot length (92.95%), root length (146.14%), secondary roots (91.23%), and chlorophyll content (−61.49%) as compared to the control (without consortia). The Na and K intake were higher even in the presence of the microbes, but the beneficial effect of the microbe helps plants sustain in the saline environment. The inoculation of microbial consortia produced more secondary roots, which accumulate more minerals and transport substances to the different parts of the plant; thus, it produced higher biomass and growth. Results of the present study revealed that the treatment with microbial consortia could alleviate the deleterious effects of salinity stress and improve the growth of tomato plants under salinity stress. Microbial consortia appear to be the best alternative and cost-effective and sustainable approach for managing soil salinity and improving plant growth under salt stress conditions.

Urban green spaces in Dhaka, Bangladesh, harbour nearly half the country’s butterfly diversity

Cities currently harbour more than half of the world’s human population and continued urban expansion replaces natural landscapes and increases habitat fragmentation. The impacts of urbanisation on biodiversity have been extensively studied in some parts of the world, but there is limited information from South Asia, despite the rapid expansion of cities in the region. Here, we present the results of monthly surveys of butterflies in three urban parks in Dhaka city, Bangladesh, over a 3-year period (January 2014 to December 2016). We recorded 45% (137 of the 305 species) of the country’s butterfly richness, and 40% of the species detected are listed as nationally threatened. However, butterfly species richness declined rapidly in the three study areas over the 3-year period, and the decline appeared to be more severe among threatened species. We developed linear mixed effect models to assess the relationship between climatic variables and butterfly species richness. Overall, species richness was positively associated with maximum temperature and negatively with mean relative humidity and saturation deficit. Our results demonstrate the importance of urban green spaces for nationally threatened butterflies. With rapidly declining urban green spaces in Dhaka and other South Asian cities, we are likely to lose refuges for threatened fauna. There is an urgent need to understand urban biodiversity dynamics in the region, and for proactive management of urban green spaces to protect butterflies in South Asia.

Locked-in and living delta pathways in the Anthropocene

Delta systems are fundamental to the persistence of large human populations, food systems and ecosystem processes. Structural changes in natural and social components of deltas, emerging from past land-use changes, have led deltas to become locked-in loosing the ability to transform back into living deltas, and making them more at risk. We propose a framework to assess whether deltas become locked-in by changes in natural or social infrastructure, by examining the dynamic coupling between population and land-use development over 300 years for 48 deltas globally. We find that 46% of the deltas are defined as living, where population, irrigation, and cropland are correlated. Of the 54% locked-in deltas, 21% show changes in natural infrastructure to cropland (n = 6) or irrigation (n = 4), and 33% (n = 16) show changes in social infrastructure. Most locked-in deltas are in Europe but also in other continents due to decoupled development of population and cropland. While, locked-in deltas due to changes in natural infrastructure have highest average risks, those with changes in social infrastructure and the living deltas have highest risks from future relative sea level rise. These results show that deltas have varying natural and social components derived from a 300 years historical perspective, which are not taken into account in risk assessments for global deltas.

Land Cover Dynamics and Mangrove Degradation in the Niger Delta Region

The Niger Delta Region is the largest river delta in Africa and features the fifth largest mangrove forest on Earth. It provides numerous ecosystem services to the local populations and holds a wealth of biodiversity. However, due to the oil and gas reserves and the explosion of human population it is under threat from overexploitation and degradation. There is a pressing need for an accurate assessment of the land cover dynamics in the region. The limited previous efforts have produced controversial results, as the area of western Africa is notorious for the gaps in the Landsat archive and the lack of cloud-free data. Even fewer studies have attempted to map the extent of the degraded mangrove forest system, reporting low accuracies. Here, we map the eight main land cover classes over the NDR using spectral-temporal metrics from all available Landsat data centred around three epochs. We also test the performance of the classification when L-band radar data are added to the Landsat-based metrics. To further our understanding of the land cover change dynamics, we carry out two additional assessments: a change intensity analysis for the entire NDR and, focusing specifically on the mangrove forest, we analyse the fragmentation of both the healthy and the degraded mangrove land cover classes. We achieve high overall classification accuracies in all epochs (~79% for 1988, and 82% for 2000 and 2013) and are able to map the degraded mangroves accurately, for the first time, with user’s accuracies between 77% and 87% and producer’s accuracies consistently above 82%. Our results show that mangrove forests, lowland rainforests, and freshwater forests are reporting net and highly intense losses (mangrove net loss: ~500 km2; woodland net loss: ~1400 km2), while built-up areas have almost doubled in size (from 1990 km2 in 1988 to 3730 km2 in 2013). The mangrove forests are also consistently more fragmented, with the opposite effect being observed for the degraded mangroves in more recent years. Our study provides a valuable assessment of land cover dynamics in the NDR and the first ever accurate estimates of the extent of the degraded mangrove forest and its fragmentation.

Assessing Po River Deltaic Vulnerability Using Earth Observation and a Bayesian Belief Network Model

Deltaic systems are broadly recognized as vulnerable hot spots at the interface between land and sea and are highly exposed to harmful natural and manmade threats. The vulnerability to these threats and the interactions of the biological, physical, and anthropogenic processes in low-lying coastal plains, such as river deltas, requires a better understanding in terms of vulnerable systems and to support sustainable management and spatial planning actions in the context of climate change. This study analyses the potential of Bayesian belief network (BBN) models to represent conditional dependencies in vulnerability assessment for future sea level rise (SLR) scenarios considering ecological, morphological and social factors using Earth observation (EO) time series dataset. The BBN model, applied in the Po Delta region in the northern Adriatic coast of Italy, defines relationships between twelve selected variables classified as driver factors (DF), land cover factors (LCF), and land use factors (LUF) chosen as critical for the definition of vulnerability hot spots, future coastal adaptation, and spatial planning actions to be taken. The key results identify the spatial distribution of the vulnerability along the costal delta and highlight where the probability of vulnerable areas is expected to increase in terms of SLR pressure, which occurs especially in the central and southern delta portion.

Coastal flooding will disproportionately impact people on river deltas

Climate change is intensifying tropical cyclones, accelerating sea-level rise, and increasing coastal flooding. River deltas are especially vulnerable to flooding because of their low elevations and densely populated cities. Yet, we do not know how many people live on deltas and their exposure to flooding. Using a new global dataset, we show that 339 million people lived on river deltas in 2017 and 89% of those people live in the same latitudinal zone as most tropical cyclone activity. We calculate that 41% (31 million) of the global population exposed to tropical cyclone flooding live on deltas, with 92% (28 million) in developing or least developed economies. Furthermore, 80% (25 million) live on sediment-starved deltas, which cannot naturally mitigate flooding through sediment deposition. Given that coastal flooding will only worsen, we must reframe this problem as one that will disproportionately impact people on river deltas, particularly in developing and least-developed economies.

Coastal river delta regions are particularly impacted by the effects of climate change, yet though these regions are densely inhabited, robust estimates of population are lacking. Here the authors use global datasets to predict the number of people and regions most threatened by flooding and extreme weather.

Deltas in Crisis: From Systems to Sophisticated Conjunctions

In recent years, threatened deltas have emerged as a significant matter of concern in numerous fields. While Earth System science and social-ecological systems focus on topics like global water circulation and sediment transport, social scientists tend to consider the problems facing particular deltas in the context of modernization or (post)-colonial development. There is nevertheless broad agreement that the delta crisis raises fundamental questions about modern approaches to infrastructure planning. Thus, environmental and sustainability scientists have come to recognize “the social” as integral to the delta crisis. This understanding of “the social,” however, takes two quite different forms. As an object of social-ecological systems research, the social is modeled alongside ecological systems. However, as a context for scientific interventions in environmental policy it appears as an obstacle to achieving sustainable delta policies. Based on a careful examination of Earth System science and associated discourses, we show that this instability of “the social”, combined with the ambition to integrate ‘it’ in an encompassing system poses serious problems for interdisciplinary delta research and for more imaginative and inclusive collaborative efforts to tackle the delta crisis—including, but going considerably beyond, policy and governance. Rather than integrative systems, we argue that the situation requires the creation of sophisticated conjunctions of epistemologies, methods, and practices. Such conjunctions, we suggest, pave the way for a cosmo-ecological approach, where social, environmental and sustainability sciences work together with designers, urban planners, policy-makers, and affected or concerned citizens on solving multi-scalar delta problems by working across their differences.

Impacts of natural and human drivers on the multi-decadal morphological evolution of tidally-influenced deltas

The world's deltas are at risk of being drowned due to rising relative sea levels as a result of climate change, decreasing supplies of fluvial sediment, and human responses to these changes. This paper analyses how delta morphology evolves over multi-decadal timescales under environmental change using a process-based model. Model simulations over 10² years are used to explore the influence of three key classes of environmental change, both individually and in combination: (i) varying combinations of fluvial water and sediment discharges; (ii) varying rates of relative sea-level rise; and (iii) selected human interventions within the delta, comprising polder-dykes and cross-dams. The results indicate that tidal asymmetry and rate of sediment supply together affect residual flows and delta morphodynamics (indicated by sub-aerial delta area, rates of progradation and aggradation). When individual drivers of change act in combination, delta building processes such as the distribution of sediment flux, aggradation, and progradation are disrupted by the presence of isolated polder-dykes or cross-dams. This suggests that such interventions, unless undertaken at a very large scale, can lead to unsustainable delta building processes. Our findings can inform management choices in real-world tidally-influenced deltas, while the methodology can provide insights into other dynamic morphological systems.

Applying the global RCP-SSP-SPA scenario framework at sub-national scale: A multi-scale and participatory scenario approach

To better anticipate potential impacts of climate change, diverse information about the future is required, including climate, society and economy, and adaptation and mitigation. To address this need, a global RCP (Representative Concentration Pathways), SSP (Shared Socio-economic Pathways), and SPA (Shared climate Policy Assumptions) (RCP-SSP-SPA) scenario framework has been developed by the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC-AR5). Application of this full global framework at sub-national scales introduces two key challenges: added complexity in capturing the multiple dimensions of change, and issues of scale. Perhaps for this reason, there are few such applications of this new framework. Here, we present an integrated multi-scale hybrid scenario approach that combines both expert-based and participatory methods. The framework has been developed and applied within the DECCMA¹ project with the purpose of exploring migration and adaptation in three deltas across West Africa and South Asia: (i) the Volta delta (Ghana), (ii) the Mahanadi delta (India), and (iii) the Ganges-Brahmaputra-Meghna (GBM) delta (Bangladesh/India). Using a climate scenario that encompasses a wide range of impacts (RCP8.5) combined with three SSP-based socio-economic scenarios (SSP2, SSP3, SSP5), we generate highly divergent and challenging scenario contexts across multiple scales against which robustness of the human and natural systems within the deltas are tested. In addition, we consider four distinct adaptation policy trajectories: Minimum intervention, Economic capacity expansion, System efficiency enhancement, and System restructuring, which describe alternative future bundles of adaptation actions/measures under different socio-economic trajectories. The paper highlights the importance of multi-scale (combined top-down and bottom-up) and participatory (joint expert-stakeholder) scenario methods for addressing uncertainty in adaptation decision-making. The framework facilitates improved integrated assessments of the potential impacts and plausible adaptation policy choices (including migration) under uncertain future changing conditions. The concept, methods, and processes presented are transferable to other sub-national socio-ecological settings with multi-scale challenges.

Changing sediment budget of the Mekong: Cumulative threats and management strategies for a large river basin

Two decades after the construction of the first major dam, the Mekong basin and its six riparian countries have seen rapid economic growth and development of the river system. Hydropower dams, aggregate mines, flood-control dykes, and groundwater-irrigated agriculture have all provided short-term economic benefits throughout the basin. However, it is becoming evident that anthropic changes are significantly affecting the natural functioning of the river and its floodplains. We now ask if these changes are risking major adverse impacts for the 70 million people living in the Mekong Basin. Many livelihoods in the basin depend on ecosystem services that will be strongly impacted by alterations of the sediment transport processes that drive river and delta morpho-dynamics, which underpin a sustainable future for the Mekong basin and Delta. Drawing upon ongoing and recently published research, we provide an overview of key drivers of change (hydropower development, sand mining, dyking and water infrastructures, climate change, and accelerated subsidence from pumping) for the Mekong's sediment budget, and their likely individual and cumulative impacts on the river system. Our results quantify the degree to which the Mekong delta, which receives the impacts from the entire connected river basin, is increasingly vulnerable in the face of declining sediment loads, rising seas and subsiding land. Without concerted action, it is likely that nearly half of the Delta's land surface will be below sea level by 2100, with the remaining areas impacted by salinization and frequent flooding. The threat to the Delta can be understood only in the context of processes in the entire river basin. The Mekong River case can serve to raise awareness of how the connected functions of river systems in general depend on undisturbed sediment transport, thereby informing planning for other large river basins currently embarking on rapid economic development.

Catastrophic healthcare expenditure and impoverishment in tropical deltas: evidence from the Mekong Delta region

BACKGROUND

Universal health coverage implies that people obtain the health services they need without experiencing financial hardship. While the factors contributing to catastrophic health expenditure (CHE) among households are well understood, few studies have examined this relationship in the context of environmentally vulnerable regions, such as tropical deltas. This study aims to examine the disparities in the prevalence of CHE and impoverishment due to out-of-pocket (OOP) healthcare payments in the Mekong Delta in comparison with rest of Vietnam. It also intends to investigate the associations between economic and environmental shocks, CHE and the impoverishment from healthcare payments.

METHODS

Using data from the Vietnam Household Living Standards Survey 2012, the prevalence of CHE was estimated from the fraction of healthcare costs in relation to household consumption expenditure. The poverty headcount was estimated using the total household consumption expenditure considering both with and without OOP expenditure for healthcare in comparison with the national poverty-line. Simple and multiple logistic regression models were used to examine the associations between geography, health systems, environmental and demographic variables and OOP healthcare expenditure related CHE, and impoverishment respectively.

RESULTS

Both the level of OOP household healthcare expenditure and the proportion of households suffering from impoverishment as the result of such payments were higher in the Mekong Delta region compared to rest of Vietnam. Although the results from the multiple regression analysis showed that households in the Mekong Delta region were significantly less likely to suffer from CHE, they were significantly more likely to be impoverished due to OOP healthcare expenditure. While health insurance membership did not have a significant effect on either outcomes, households that faced an economic or an environmental shock in past 5 years were considerably more likely to suffer from CHE and impoverishment from OOP healthcare payments.

CONCLUSIONS

The findings suggest that the financial protection capacity of health insurance schemes in Vietnam should be improved and expanded to reduce impoverishment as the result of OOP healthcare payments, particularly in the Mekong Delta region. Additional investments in disaster preparedness strategies can further help to reduce the financial burden of households in this environmentally vulnerable region.

Entropy and optimality in river deltas

River deltas are critically important Earthscapes at the land–water interface, supporting dense populations and diverse ecosystems while also providing disproportionately large food and energy resources. Deltas exhibit complex channel networks that dictate how water, sediment, and nutrients are spread over the delta surface. By adapting concepts from information theory, we show that a range of field and numerically generated deltas obey an optimality principle that suggests that deltas self-organize to increase the diversity of sediment transport pathways across the delta channels to the shoreline. We suggest that optimal delta configurations are also more resilient because the same mechanism that diversifies the delivery of fluxes to the shoreline also enhances the dampening of possible perturbations.

The form and function of river deltas is intricately linked to the evolving structure of their channel networks, which controls how effectively deltas are nourished with sediments and nutrients. Understanding the coevolution of deltaic channels and their flux organization is crucial for guiding maintenance strategies of these highly stressed systems from a range of anthropogenic activities. To date, however, a unified theory explaining how deltas self-organize to distribute water and sediment up to the shoreline remains elusive. Here, we provide evidence for an optimality principle underlying the self-organized partition of fluxes in delta channel networks. By introducing a suitable nonlocal entropy rate (nER) and by analyzing field and simulated deltas, we suggest that delta networks achieve configurations that maximize the diversity of water and sediment flux delivery to the shoreline. We thus suggest that prograding deltas attain dynamically accessible optima of flux distributions on their channel network topologies, thus effectively decoupling evolutionary time scales of geomorphology and hydrology. When interpreted in terms of delta resilience, high nER configurations reflect an increased ability to withstand perturbations. However, the distributive mechanism responsible for both diversifying flux delivery to the shoreline and dampening possible perturbations might lead to catastrophic events when those perturbations exceed certain intensity thresholds.

Sounding the Alarm: Health in the Anthropocene

There is growing scientific and public recognition that human actions, directly and indirectly, have profoundly changed the Earth system, in a still accelerating process, increasingly called the "Anthropocene". Planetary transformation, including of the atmosphere, climate, ecosystems and biodiversity, has enormous implications for human health, many of which are deeply disturbing, especially in low-income settings. A few health consequences of the Anthropocene have been partially recognized, including within environmental epidemiology, but their long-term consequences remain poorly understood and greatly under-rated. For example Syria could be a "sentinel" population, giving a glimpse to a much wider dystopian future. Health-Earth is a research network, co-founded in 2014, which seeks, with other groups, to catalyse a powerful curative response by the wider health community. This paper builds on a symposium presented by Health-Earth members at the 2015 conference of the International Society for Environmental Epidemiology. It reviews and synthesizes parts of the large literature relevant to the interaction between the changing Earth system and human health. It concludes that this topic should be prominent within future environmental epidemiology and public health. Created by our species, these challenges may be soluble, but solutions require far more understanding and resources than are currently being made available.